Glutamine auxotrophs of Salmonella typhimurium have mutations in at least two chromosomal loci in addition to the structural gene encoding the glutamine synthetase subunit, glnA. Mutations at the glnF, glnG (and glnH?) loci apparently interfere with synthesis of glutamine synthetase. We will attempt to identify the products of these regulatory genes by means of a biochemical and genetic analysis of mutant strains; in particular, we will determine whether they encode components of the adenylylation-deadenylylation cascade responsible for covalent modification of glutamine synthetase (as is the case in K. aerogenes (2)) or whether one of them might encode an activator of transcription of the glnA gene. In addition, we will attempt to define the operator-promoter region glnO adjacent to the glnA gene. We will determine whether the glnA gene constitutes an operon with structural genes encoding glutamine transport components (particularly a periplasmic glutamine-binding protein); if this is the case, characterization of the glnO region will be facilitated. Unlike Klebsiella, Salmonella strains lack nitrogen control of transcription of genes for various degradative enzymes, e.g. the histidine utilization (hut) genes. (In this sense Salmonella appears to be a "mutant" of Klebsiella). We will attempt to transduce the nitrogen control of Klebsiella into Salmonella using phage P1kc and to determine whether this control is mediated by glutamine synthetase (1) or by another essential regulatory element that is absent in Salmonella. In collaboration with Dr. K. Krohn, we will develop methods to study the transport and assimilation of radioactive 13N-labeled ammonia by wild-type Salmonella and mutant strains (nit) with pleiotropic defects in nitrogen metabolism. Defects in these strains suggest that they may have a lesion in transport of ammonium ion at low concentrations.